I need to render an object in a different material, @FFeller, helped me with the index material geometry node, which allowed me to automate the rendering. But, in the naming the rendered images, didn’t include the material names.
Knowing that I had almost 50 different materials, that I already properly named in a slot material, you can imagine what time-consuming renaming all the images….

And I’m not familiar with python, so is there any help…. Thankx

PS: screenshot to illustrate my question 
[![enter image description here][1]][1]
[![enter image description here][2]][2]


@Marty Fouts, 

[![enter image description here][3]][3]
[![enter image description here][4]][4]
[![enter image description here][5]][5]


 [1]: https://i.sstatic.net/Yyw4w.png
 [2]: https://i.sstatic.net/L1BK6.png
 [3]: https://i.sstatic.net/3FUy7.png
 [4]: https://i.sstatic.net/7PqvB.png
 [5]: https://i.sstatic.net/Us84q.png